Improving the Validation and Prediction of Tropical Cyclone Rainfall

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Improving the Validation and Prediction of
Tropical Cyclone Rainfall

• Timothy Marchok
• NOAA / GFDL
• Robert Rogers
• NOAA / AOML / HRD
• Robert Tuleya
• NOAA / NCEP / EMC / SAIC
• Additional Collaborator Manuel Lonfat, Risk
  Management Solutions

This project was funded by the Joint Hurricane
Testbed (JHT)
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Goals

• Develop a set of rainfall validation schemes
  specifically designed for TCs
• Produce model QPF error statistics for a set of
  historic U.S. landfalling storms.
• Develop a forecasting tool based on R-CLIPER that
  utilizes vertical shear forecast data and the
  effect of topography.

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Outline

• Models storms
• Development of TC QPF validation techniques
• 1998-2004 base sample vs. 2005 season
• Skill indices based on new techniques
• New forecasting tool based on R-CLIPER

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Models included in this study
GFDL
Regional 1/2o, 1/6o
(2-nest) 42 levels
2003 version
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U.S. Landfalling Cases for Model
Evaluation1998-2004 Base Sample
2004
2003
2002
2001
2000
1999
1998
2004
2003
2002
2001
2000
1999
1998
Bonnie
Bill
Bertha
Allison
Gordon 55
Bret
Bonnie
Bonnie
Bill
Bertha
Allison
Gordon 55
Bret
Bonnie
45
45
50
35
45
100
95
50
35
45
100
95
Charley
Claudette
Edouard
Barry
Helene
Dennis
Charley 40
Charley
Claudette
Edouard
Barry
Helene
Dennis
Charley 40
125
125
75
35
60
65
60
75
35
60
65
60
Frances
Grace
Fay
Gabrielle 60
Floyd
Earl
Frances
Grace
Fay
Gabrielle 60
Floyd
Earl
95
95
35
50
90
70
35
50
90
70
Gaston
Henri
Hanna
Harvey
Frances
Gaston
Henri
Hanna
Harvey
Frances
65
65
30
45
50
45
30
45
50
45
Ivan
Isabel
Isidore
Irene
Georges
Ivan
Isabel
Isidore
Irene
Georges
110
110
90
55
70
90
90
55
70
90
Jeanne
Kyle
Hermine
Jeanne
Kyle
Hermine
105
105
35
35
35
35
Matthew
Lili
Matthew
Lili
40
40
85
85
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U.S. Landfalling Cases for Model Evaluation2005
Season

• Arlene
• Cindy
• Dennis
• Katrina (Florida)
• Katrina (Louisiana)

• Ophelia
• Rita
• Tammy
• Wilma

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Outline

• Models storms
• Development of TC QPF validation techniques
• 1998-2004 base sample vs. 2005 season
• Skill indices based on new techniques
• New forecasting tool based on R-CLIPER

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Parameters describing skill of TC QPF forecasts

• Rainfall patterns
• Rainfall volume
• Extreme amounts
• Sensitivity to track errors

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Rainfall patterns
2005
1998-2004
Equitable threat score comparison
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Rainfall volume
Example Tropical Storm Cindy (2005)
Stage IV (Observed)
GFS
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Rainfall volume
Comparison of rain volume bias by model
2005
1998-2004
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Rainfall volume Rain flux and track-relative
analyses
Observed rain flux PDF for all 1998-2004 storms
in selected bands surrounding best track
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Rain volume Rain flux in select bands
GFS, R-CLIPER
GFDL, NAM
0100 km
300-400 km
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Extreme amounts Comparison of top 5 of rain flux
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Sensitivity to track error
Example of grid-shifting of rain field
Lili Stage IV
r increased from 0.36 (unshifted) to 0.85
(shifted)
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Sensitivity to track error
Impact of grid shift on pattern correlations
1998-2004
2005
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Outline

• Models storms
• Development of TC QPF validation techniques
• 1998-2004 base sample vs. 2005 season
• Skill indices based on new techniques
• New forecasting tool based on R-CLIPER

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Matrix of TC QPF Skill Indices
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Skill Indices Pattern Matching
1998-2004
2005

• GFS performs the best in both samples
• All models have skill relative to R-CLIPER

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Skill Indices Volume
1998-2004
2005

• R-CLIPER significantly better in 2005 season
• GFS worse in 2005 due to over-forecast bias

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Skill Indices Extreme Amounts
2005
1998-2004

• GFDL worse in 2005 due to core region
  over-forecast bias
• GFS performs best despite lowest resolution

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Skill Indices Sensitivity to track error
2005
1998-2004
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Outline

• Models storms
• Development of TC QPF validation techniques
• 1998-2004 base sample vs. 2005 season
• Skill indices based on new techniques
• New forecasting tool based on R-CLIPER

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Building on R-CLIPER Inclusion of vertical shear
forecast data topography
Formulation
Rtot(r,?) a0(r)
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Example of shear footprint Hurricane Ivan
b) Contribution from Wavenumbers 1,2
a) Contribution from Wavenumber 0
c) Shear footprint is stamped on a lon/lat grid
every 15 minutes, providing a contribution to
storm total accumulation
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Stage IV
R-CLIPER
R-CLIPER Shear Topog
R-CLIPER Shear
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Examples of R-CLIPER / SHRAPS validations
Equitable Threat Score
Rain flux CDF
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Summary

• Developed QPF validation schemes specific for
  unique characteristics of TC rainfall.
• Developed TC QPF skill indices to allow for
  objective year-to-year comparisons of operational
  TC rainfall forecasts.
• Used the new techniques to provide TC QPF
  statistics for a baseline 1998-2004 sample as
  well as for the 2005 season.
• Developed a forecasting tool based on R-CLIPER
  that includes the effects of vertical shear and
  topography.

Additional work

• Work with TPC to automate R-CLIPER forecasts and
  allow for transmission of forecast data via NWS
  AWIPS network.
• Implement SHRAPS version with both shear
  topography
• Streamline the TC QPF validation system to
  facilitate easier end-of-season TC rainfall
  verification.

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Extra slides..
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Rainfall volume
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Rain volume GFDL NAM rain flux in select bands
0 100 km
300-400 km
1998 - 2004
2005